function box(_x,_y,_w,_h)
 return{
 x=_x,
 y=_y,
 w=_w,
 h=_h
 }
end

function get_cols(a)
 local gx,gy=flr(a.x/8),flr(a.y/8)
 local ex,ey=flr((a.x+a.w-1)/8),flr((a.y+a.h-1)/8)

 local list={}
 for i=gx-1,ex+1 do
  for ii=gy-1,ey+1 do
   if fget(mget(i,ii),0) then
    add(list,box(i*8,ii*8,8,8))
   end
  end
 end

 return list
end

function collide(a,_dx,_dy,list,side)

 local ca={
  x=flr(a.x),
  y=flr(a.y),
  w=a.w,
  h=a.h
 }

 for i=1,#list do
  local v=list[i]

  if col(v,ca) then
   if _dx>0 then
    a.x=v.x-a.w
    side["right"]=true
   elseif _dx<0 then
    a.x=v.x+v.w
    side["left"]=true
   end

   if _dy>0 then
    a.y=v.y-a.h
    side["down"]=true
   elseif _dy<0 then
    a.y=v.y+v.h
    side["up"]=true
   end

  end

 end

end

--diss code expects that "a" have a
--dx and dy 

function move(a)

 local sides={
  ["left"]=false,
  ["right"]=false,
  ["up"]=false,
  ["down"]=false
 }
 local l=get_cols(a)

 a.x+=a.dx
 collide(a,a.dx,0,l,sides)
 a.y+=a.dy
 collide(a,0,a.dy,l,sides)

 if sides["up"] or sides["down"] then
  a.dy=0
 end 

 if sides["left"] or sides["right"] then
  a.dx=0
 end 

 return sides
end

function col(a,b)
 return not(
 (a.x>b.x+b.w-1)or
 (b.x>a.x+a.w-1)or
 (a.y>b.y+b.h-1)or
 (b.y>a.y+a.h-1)
 )
end